MAGNETIC STORMS.
The mysterious course of the magnetic needle is equally affected by time and space, by the sun’s course, and by changes of place on the earth’s surface. Between the tropics the hour of the day may be known by the direction of the needle as well as by the oscillations of the barometer. It is affected instantly, but transiently, by the northern light.
When the uniform horary motion of the needle is disturbed by a magnetic storm, the perturbation manifests itself simultaneously, in the strictest sense of the word, over hundreds and thousands of miles of sea and land, or propagates itself by degrees in short intervals every where over the earth’s surface.
Among numerous examples of perturbations occurring simultaneously and extending over wide portions of the earth’s surface, one of the most remarkable is that of September 25th, 1841, which was observed at Toronto in Canada, at the Cape of Good Hope, at Prague, and partially in Van Diemen’s Land. Sabine adds, “The English Sunday, on which it is deemed sinful, after midnight on Saturday, to register an observation, and to follow out the great phenomena of creation in their perfect development, interrupted the observation in Van Diemen’s Land, where, in consequence of the difference of the longitude, the magnetic storm fell on Sunday.”
It is but justice to add, that to the direct instrumentality of the British Association we are indebted for this system of observation, which would not have been possible without some such machinery for concerted action. It being known that the magnetic needle is subject to oscillations, the nature, the periods, and the laws of which were unascertained, under the direction of a committee of the Association magnetic observatories were established in various places for investigating these strange disturbances. As might have been anticipated, regularly recurring perturbations were noted, depending on the hour of the day and the season of the year. Magnetic storms were observed to sweep simultaneously over the whole face of the earth, and these too have now been ascertained to follow certain periodic laws.
But the most startling result of the combined magnetic observations is the discovery of marked perturbations recurring at intervals of ten years; a period which seemed to have no analogy to any thing in the universe, but which M. Schwabe has found to correspond with the variation of the spots on the sun, both attaining their maximum and minimum developments at the same time. Here, for the present, the discovery stops; but that which is now an unexplained coincidence may hereafter supply the key to the nature and source of Terrestrial Magnetism: or, as Dr. Lloyd observes, this system of magnetic observation has gone beyond our globe, and opened a new range for inquiry, by showing us that this wondrous agent has power in other parts of the solar system.